When people move from place to place they often need to keep up to date on the resulting changes in their perspectives, that is, on the distances and directions relating them to features of the surroundings. Adults can keep up to date on such changes without spotting them visually when, for example, the features are occluded from view or the place is dark or the observer is blind. The present experiments are about the precision of infants' and young children's perceptions of self-movement and their abilities to act on them when searching for objects in the dark and in other situations where they are occluded from view. The experiments are focused on the period in life when children make the transition from infancy to early childhood, and on the role played by locomotion and perception in that transition. We devised a behavioral test and adapted psychophysical methods to assess individual levels of sensitivity to threshold changes in self- to-object directions for 1 to 5 year olds after they move to new points of observation. The proposal is to estimate individual children's threshold levels of sensitivity as a function of variations in the self-movements and the environmental reference information in a series of cross sectional experiments, and as a function of experimentally controlled variations in the children's locomotor experiences in a 20 month long longitudinal observation. Locomotor search games are used to estimate children's sensitivity. The self-movement variables are the movement's geometry (rotations, translations), distance, and complexity. The reference information variables are the presence or absence of visual information, auditory information, and leg information from walking versus riding a trolly. The organismic variables include variations in walking experience induced through the random assignment of children to groups using mechanical walkers and not using them in their homes.